The processing of photosensitive material involves a series of steps such as developing, bleaching, fixing, washing, and drying. These steps lend themselves to mechanization by conveying a continuous web of film or cut sheets of film or photographic paper sequentially through a series of stations or tanks, each one containing a different processing liquid appropriate to the process step at that station.
There are various sizes of photographic film processing apparatus, i.e., large photofinishing apparatus and microlabs. A large photofinishing apparatus utilizes tanks that contain approximately 100 liters of each processing solution. A small photofinishing apparatus or microlab utilizes tanks that may contain less than 10 liters of processing solution.
Typically large photofinishing apparatus and microlabs utilize fixed and integrated horizontal and vertical arrangements of racks and tanks, i.e., the stations. Each station must be maintained at predetermined temperatures for permitting proper processing at that particular station. The first station into which the photographic paper enters is typically the developer which requires the variance of the temperature to be small in comparison with the other stations. The other stations of wider temperature variance usually function as a heat sink for the developer, which has a tendency to overheat. To cool the developer for maintaining the desired temperature, some of its processing solution is suctioned into a heat exchange conduit which passes through the other stations for heating the other stations and cooling the developer, such as that disclosed in U.S. Pat. No. 4,994,837.
Although the above-described system and method for heat exchange is satisfactory, it is not without drawbacks. The heat exchange is obviously constrained by the fluid temperature passing through the heat exchanger which is not controlled independent of the temperature of the processing solutions in the developer station. Consequently, a need exists for a thermal control arrangement that overcomes the above-described drawbacks.